How to Always Secure Empty Trash
You can set Mac OS X to always securely empty the Trash just by adjusting a preference within the Finder. Here’s how:
* Enter the Finder Preferences by either going to the Finder menu and selecting “Preferences” or by hitting Command+, within the Finder.
* Click on the ‘Advanced’ tab icon
* Click the checkbox next to “Empty Trash Securely”
Now your Trash will always be securely emptied! Note this makes data recovery practically impossible.

I found that when the OS was empting the Trash Can it was taking up alot of CPU so I use a app called the Trash Can which over writes everything in the Trash Can seven times but does’nt take large amounts of CPU to cpmplete it’s task.
I take a slightly different approach. I created a folder on my desktop called “Shredder” where I dump stuff I want to disappear permanently. When I get good and ready, I run a simple shell script that executes:
rm -Prv ~/Desktop/Shredder/*
which overwrites and then deletes everything I put in the shredder. (I suppose I could put an Automator or AppleScript icon on the desktop to do this, but so far this scheme is so simple that I haven’t.)
This works extremely fast, and only shreds really confidential stuff that you put in the Shredder.
This is not at all the same as “Secure Empty Trash.” There’s a reason it requires much more CPU time.
http://en.wikipedia.org/wiki/Srm_%28Unix%29
The -P switch is certainly an improvement over a simple rm. I’m not suggesting the above is a poor solution for everyone. But it’s not as thorough as secure empty trash.
A great tip there, and an equally great follow-up from Art Westin.
I’m just securely emptying my trash and it’s taking a while, so I’ll bear that line of script in mind for future removals.
Cheers.
Doesn’t this just put a secure delete button in trash?
I prefer to leave the button as just “empty” for deleting safe files, as it’s overkill to use secure delete for those (& uses all the CPU). I choose “secure delete” from the finder menu when I really need it.
You can use a keyboard shortcut when this is enabled, though I prefer the above method.
In Lion (and possibly Leopard) when you right click the trash can, you can press Cmd to show the “Secure Empty Trash” option.
[...] you’re in the Advanced Finder preferences, you might want to enable the always “Empty Trash securely” feature as well, just be aware that it makes the recovery of any data deleted practically [...]